Single-sided triple layer optical disc

ABSTRACT

An optical disc is based on the following the distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm. The distance between the first and the third recording layer is a maximum of 72 μm. The distance between the second and the third recording layer is a minimum of 15 μm. The distance between the first and the second recording layer is about 31 to 40 μm. The reflectivities of the first and the second recording layer with respect to the first laser beam are 18% or more, and the ratio between the reflectivities is about 1.15 or less. The areal recording density of the third recording layer is three times or more as high as the areal recording density of the first and the second recording layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-237741, filed Aug. 18, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the invention relates to an optical disc such as a DVD which serves as a medium to store digitized video and audio works such as movies and music. It further relates to an optical disc apparatus which reads information recorded on the optical disc, and a digital work publication using the optical disc as a recording medium.

2. Description of the Related Art

<Outline of the DVD Standard>

One known type of optical disc for storing digital images is a Digital Versatile Disc (DVD), which has been widely used all over the world mainly in storing and delivering movie content (digital work publications). This DVD is a format created by the DVD Forum, which is open to the public as DVD Book (refer to the World Wide Web: dvdforum.org). The DVD has also been determined in international standards and JIS. Here, the international standard ISO/IEC 16448 for 120 mm DVD-ROM, one of the DVD physical formats, will be briefly explained. Moreover, there is ECMA-267 as a document associated with the international standards.

There are four types of 120 mm DVD-ROM: single-sided single layer, single-sided dual layer, double-sided single layer, and double-sided dual layer. In delivery of an accumulation of content of movies and the like, two types of single-sided discs are mainly used: one is a single-sided single layer DVD disc (4.7 GB) and the other is a single-sided dual layer DVD disc (8.54 GB). However, recently, the single-sided dual layer DVD disc has accounted for 60% of the total.

On the other hand, the development of a disc whose capacity is larger than that of the aforementioned DVD (referred to as the existing DVD) has been desired. This comes from a desire to store High Definition (HD) images into a single disc (temporarily referred to as a next-generation DVD).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.

FIG. 1 is an exemplary diagram showing the relationship between the basic structure of a single-sided dual layer DVD disc and an optical head;

FIG. 2 is an exemplary diagram showing the position of the recording layers of the single-sided dual layer DVD disc;

FIG. 3 is an exemplary diagram showing the relationship between the basic structure of a single-sided dual layer HD DVD disc and an optical head;

FIG. 4 is an exemplary diagram showing the position of the recording layers of the single-sided dual layer HD DVD disc;

FIG. 5 is an exemplary diagram showing the relationship between the basic structure of an HD DVD/DVD Twin format disc and an optical head;

FIG. 6 is an exemplary diagram showing the position of the recording layers in the HD DVD/DVD Twin format disc;

FIG. 7 is an exemplary diagram showing the relationship between the basic structure of an optical disc of the present invention and an optical head;

FIG. 8 is an exemplary diagram showing one example of how to design the thickness of substrates and interlayer thickness of the optical disc of the present invention;

FIGS. 9A and 9B are diagrams showing actual measurement values of the reflectivity and transmissivity of an Ag alloy film;

FIGS. 10A and 10B are diagrams showing calculated values of the reflectivity and transmissivity of the Ag alloy film;

FIG. 11 is an exemplary diagram showing the reflectivities of layers of the optical disc of the present invention with respect to a red laser beam;

FIG. 12 is an exemplary diagram showing the reflectivities of the layers of the optical disc of the present invention with respect to a blue-violet laser beam;

FIG. 13 is an exemplary diagram showing the configuration of a player complying with the DVD standard;

FIG. 14 is an exemplary diagram showing an operation flow when the optical disc of the present invention is played back with a red laser beam on the player complying with the DVD standard;

FIG. 15 is an exemplary diagram showing the relationship between focus signals and a focus servo when the optical disc of the present invention is played back with a red laser beam on the player complying with the DVD standard;

FIG. 16 is an exemplary diagram showing the configuration of an HD DVD player complying with the optical disc of the present invention;

FIG. 17 is an exemplary diagram showing an operation flow when the optical disc of the present invention is played back on the HD DVD player complying with the optical disc of the present invention;

FIG. 18 is an exemplary diagram showing the relationship between focus signals and a focus servo when the optical disc of the present invention is played back with a blue-violet laser beam on the HD DVD player complying with the optical disc of the present invention;

FIG. 19 is an exemplary diagram showing the configuration of an HD DVD/DVD compatible player complying with the optical disc of the present invention; and

FIG. 20 is an exemplary diagram showing an operation flow of the DVD/DVD compatible player complying with the optical disc of the present invention.

DETAILED DESCRIPTION

Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings.

If a next-generation DVD is developed, a conventional DVD device (drive or player) can not read data from the next-generation DVD since the next-generation DVD is substantially different from the existing DVD in recording density, modulation system, signal processing, track format, and the like. That is, the conventional DVD device has the disadvantage of being unable to read conventional DVD movie content recorded on the next-generation DVD disc as well as high definition movie content recorded on the next-generation DVD disc, which may lead to a factor that hinders the spread of the next-generation DVD.

Furthermore, since single-sided dual layer DVD discs account for 60% of all the existing DVD discs, there is a desire for a new next-generation disc which can be treated as if the single-sided dual layer DVD disc is treated.

Thus, in this embodiment, a single disc can deal with not only information (content) in an HD DVD but also information (content) in a single-sided dual layer DVD.

This one embodiment is based on the configuration of a single-sided triple layer optical disc comprising: a light transmission layer; a first recording layer and a second recording layer which are accessed with a first laser beam; and a third recording layer which is accessed with a second laser beam, these layers being arranged in that order in a direction in which the laser beams enter, wherein the distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm, the distance between the first recording layer and the third recording layer is a maximum of 72 μm, the distance between the second recording layer and the third recording layer is a minimum of 15 μm, and the areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer.

Hereinafter, referring to the drawings, embodiments of the present invention will be explained. To make it easier to understand the present invention, the technologies of the existing DVD and the next-generation DVD will be explained using FIGS. 1 to 6. Then, the basic configuration of a next-generation DVD according to the present invention will be explained using FIG. 7.

<Single-sided Dual Layer DVD>

FIG. 1 shows the relationship between the basic structure of a single-sided dual layer DVD disc 10 and an optical head. As is well known, this disc has a DVD layer (L0) 15 and a DVD layer (L1) 17. The two DVD layers can be accessed from one side of the disc, thereby reproducing a signal. As shown in FIG. 1, when viewed from a light incidence plane 11, there are arranged a light transmission layer 14, the DVD layer (L0) 15, and the DVD layer (L1) 17 in that order. The individual DVD layers are accessed by moving an objective lens 21 under the control of a lens actuator and performing a layer jump.

The dual layer disc is mainly characterized in that it can be produced in about the same manner as a single-sided single layer DVD disc. First, there are separately produced, by use of an injection molding machine, an L0 substrate 12 where the DVD layer (L0) 15 is formed, and an L1 substrate 13 where the DVD layer (L1) 17 is formed. Next, a low reflection film is formed to the DVD layer (L0) 15, and a high-reflectivity film is formed to the DVD layer (L1) 17. Then, the two substrates are bonded together with a space layer 16 in such a manner that the DVD layers lie between the two substrates, which completes the disc. It is to be noted that a spiral direction of a track formed in the L1 substrate 13 is opposite to a spiral direction of a track formed in the L0 substrate 12, but after the bonding, they are in the same direction when viewed from the light incidence plane 11.

FIG. 2 is a diagram showing the position of the DVD layers when viewed from the light incidence plane 11 of the single-sided dual layer DVD disc. The DVD layer (L0) 15 is limited to a position a minimum of 550 μm away from the light incidence plane, and the DVD layer (L1) 17 is limited to a position a maximum of 640 μm away from the light incidence plane, taking into account the spherical aberration of the objective lens and crosstalk between the DVD layers. The distance between the two layers (space layer 16) is set at 40 to 70 μm in terms of the layer crosstalk. The space layer 16 is generally equal to the thickness of an adhesive layer with which the two substrates are bonded together. In an actual manufacture, the distance is determined, taking into account the bonding accuracy and the formation accuracy of the L0 substrate 12. It is to be noted that the linear recording density is reduced by 10% as compared with a single-sided single layer DVD disc and the capacity per layer is 4.27 GB. Jitter is regulated to be below 8.0%.

On the other hand, the reflectivities of the DVD layers are determined as follows:

Single-layer disc: 45% to 85% (with PBS)

Dual layer disc: 18% to 30% (with PBS)

Identification information indicating the reflectivity, layer structure and the like of the disc is in Identification Data (ID) of a Data frame and in Physical Format Information (PFI) in a Control Data Zone (CDZ) located in a Lead-in area of the DVD layer (L0) 15. It is to be noted that a Burst Cutting Area (BCA) can not be formed in a DVD video in which images are dealt with.

<HD DVD>

On the other hand, as has been often reported in recent years, an HD DVD has been proposed wherein blue-violet semiconductor laser (hereinafter, referred to as blue-violet laser) is used to achieve a density three times or more as high as that of DVD in order to satisfy a desire to store High Definition (HD) images onto a single disc. The HD DVD has been standardized in the DVD Forum (refer to the World Wide Web: dvdforum.org). This has not been commercialized yet.).

The HD DVD has the same disc structure as that of a conventional DVD. A single-sided single layer HD DVD disc has a capacity of 15 GB and a single-sided dual layer HD DVD disc has a capacity of 30 GB. These large capacities have been realized by new technologies, including a shorter wavelength of laser light, a larger NA, a modulation system, and new signal processing (partial response and maximum likelihood PRML).

FIG. 3 shows the relationship between the basic structure of a single-sided dual layer HD DVD disc 30 and an optical head. In the HD DVD, a laser beam for reading information from the disc has been changed from a red laser beam (650 nm) to a blue-violet laser beam (405 nm) 40 to have a shorter wavelength, and NA of an objective lens 41 has increased from 0.6 to 0.65, resulting in a different spherical aberration and a different coma aberration caused by a tilt. Therefore, an actual disc is different from the DVD, for example, in terms of the position of an HD DVD layer (L0) 35 and an HD DVD layer (L1) 37 from a light incidence plane 31 and in terms of the thickness of a space layer 36.

FIG. 4 shows the position of the layers of the single-sided dual layer HD DVD disc when viewed from the light incidence plane 31. Since the spherical aberration has become severer as a result of making the wavelength shorter and NA larger, the HD DVD layer (L0) 35 is limited to a position a minimum of 578 μm away from the light incidence plane and the HD DVD layer (L1) 37 is limited to a position a maximum of 622 μm away from the light incidence plane. The distance between the two layers (space layer 36) is set to be 15 to 25 μm.

On the other hand, the reflectivities of the HD DVD layers are determined as follows:

Single-layer disc: 40% to 70% (including birefringence)

Dual layer disc: 18% to 32% (including birefringence)

As in a DVD, identification information indicating the reflectivity, layer structure and the like of the disc is in Identification Data (ID) of a Data frame and in Physical Format Information (PFI) in a Control Data Zone (CDZ) located in a System Lead-in area of the DVD layer (L0) 35. In addition, in the HD DVD, identification information, content protection information and the like for the disc are provided in a Burst Cutting Area (BCA) formed inside the Lead-in area. This BCA is formed in the HD DVD layer (L1) 37.

<Existing DVD and HD DVD>

Thus, the high-capacity HD DVD capable of storing HD images has been proposed. An HD DVD device (drive or player) newly designed for the HD DVD can be designed to be able to read data from not only an HD DVD disc but also a DVD. However, since this HD DVD disc is substantially different from the existing DVD in the recording density, modulation system, signal processing, track format, and the like, a conventional DVD device (drive or player) can not read information recorded thereon. That is, the conventional DVD device has the disadvantage of being unable to read not only the high definition movie content recorded on the HD DVD disc but also the conventional DVD movie content. In order to cope with the problem, an HD DVD/DVD Twin format disc having an HD DVD recording layer and a DVD recording layer has recently been standardized in the HD DVD format (refer to the World Wide Web: dvdforum.org).

<HD DVD/DVD Twin Format Disc>

The twin format disc is a new disc which can be treated as a DVD disc in the conventional DVD device and can be treated as an HD DVD disc in the HD DVD device. Moreover, if a device compatible with both the formats is used, this disc permits information (such as content) in both the formats to be selected by a user and read.

FIG. 5 shows the relationship between the basic structure of an HD DVD/DVD Twin format disc and an optical head. A Twin format disc 50 comprises a DVD substrate 52 where a DVD layer is formed, an HD DVD substrate 53 where an HD DVD layer is formed, and a space layer 56. When viewed from a light incidence plane 51, there are formed a DVD layer 55 and an HD DVD layer 57 in this order.

FIG. 6 shows the relationship of the position of the recording layers in the Twin format disc. From the light incidence plane 51, the DVD layer 55 is positioned 550 to 575 μm and the HD DVD layer 57 is positioned 578 to 622 μm, while the interlayer 56 extends from 33 to 47 μm therebetween. It is to be noted that the maximum distance between the DVD layer 55 and the HD. DVD layer 57 is 72 μm.

Furthermore, the reflectivity of this disc when read with a red laser beam is regulated as follows:

DVD layer: 45% or more

HD DVD layer: below 8%

In the current single-sided single layer DVD, there is no definition of layer crosstalk, but crosstalk from the HD DVD layer is regulated so that it can be successfully read by the current DVD devices (if the layer crosstalk is close to 8%, information can not be read by some players).

On the other hand, the reflectivity when reading with a blue-violet laser beam is regulated as follows:

HD DVD layer: 14 to 28%

As just described, the twin format disc has been standardized in the HD DVD format, such that the conventional DVD device can also read the DVD information.

Identification information indicating the reflectivity, layer structure and the like of this disc is in the DVD layer 55 and the HD DVD layer 57. Moreover, in the HD DVD layer 57, a BCA is formed inside the lead-in area.

However, since the single layer DVD disc is defined in this twin format disc, there is a problem that it is not possible to record content produced for the dual layer DVD discs which constitute the majority of the actual market.

Therefore, the present inventors have devised an optical disc, an optical disc apparatus, an optical disc reproducing method, and a digital work publication using the optical disc as a medium which enable a single disc to deal with not only the information (content) in the HD DVD but also the information (content) in the single-sided dual layer DVD. Hereinafter, specific embodiments thereof will be explained.

<Basic Configuration of an Optical Disc>

FIG. 7 shows the relationship between an optical disc according to one embodiment of the present invention and an optical head. In an optical disc 70, there are formed, from a light incidence plane 71 in order, a first signal substrate 72, a first recording layer (DVD layer (L0)) 75, a first space layer 76, a second recording layer (DVD layer (L1)) 77, a second space layer 80 and a third recording layer (HD DVD layer (L2)) 81. Data is read from the DVD recording layers (L0) 75 and (L1) 77 through an objective lens 21 with a red laser beam 20, and data is read from the HD DVD layer (L2) through an objective lens 41 with a blue-violet laser beam 40.

FIG. 8 is a diagram showing one example of how to design the thickness of substrates and space layer thickness from the light incidence plane 71 to the respective recording layers. From the light incidence plane 71, the DVD layer (L0) 75 is located a minimum of 550 μm, while the HD DVD layer (L2) 81 is located a maximum of 622 μm. Thus, an allowable distance between the two layers is a maximum of 72 μm. The three recording layers including the DVD layers (L0) and (L1) and the HD DVD layer (L2) can be arranged within 72 μm in such a manner as to satisfy their standards in a range which permits practical manufacture.

In the current DVD standard, the space layer distance of the dual layer DVD disc is a minimum of 40 μm, while the space layer distance of the dual layer HD DVD disc is a minimum of 15 μm. If these distances are subtracted from 72 μm, there remains a room of 17 μm. The accuracy of manufacturing the first signal substrate 72, the first space layer 76 and the second space layer 80 has to be covered within 17 μm.

However, in the current manufacturing technique, the accuracy in the injection molding of the first signal substrate can be about ±8 μm given the manufacturing accuracy of a stamper and attachment accuracy. Naturally, it is considered that the accuracy can be further increased in the future. On the other hand, when the DVD recording layer (L1) 77 is formed at about 30 to 40 μm on the DVD layer (L0) via the first space layer 76 by use of a 2P method, the current technique permits an accuracy of about ±2 μm. Moreover, when the second space layer 80 of about 15 to 20 μm is used to bond the first signal substrate 72 where the DVD layers are formed to the HD DVD layer (L2) 81 formed on a second signal substrate 73, a recent vacuum bonding technique permits an accuracy of about ±2 μm. These manufacturing tolerances when combined add up to 24 μm, so that there is a shortage of about 7 μm (=17 μm-24 μm) considering the practical manufacture.

This is presently one of the reasons that two DVD layers can not be provided in the HD DVD/DVD twin format disc.

It has been found out that limiting the ratio between the reflectivities of the DVD layers permits the space layer distance to be reduced to some extent without increasing the layer crosstalk, and the present invention has been made under this fact.

FIG. 8 shows one practical example of the positional relation among the recording layers of the present invention. In the present invention, the ratio between the reflectivities of the DVD layers (L0) 75 and (L1) 77 is limited to about 1.15 to reduce the minimum value of the first space layer 76 to about 33 μm. As a result, the first space layer 76 is 33 to 37 μm, and the second space layer 80 is 15 to 19 μm, so that, from the light incidence plane 71, the DVD layer (L0) 75 is located 558±8 μm, the DVD layer (L1) 77 is located 593±10 μm, and the HD DVD layer (L2) 81 is located 610±12 μm. Thus, three recording layers can be formed in one disc: the layers of the single-sided dual layer DVD and the HD DVD.

<Layer Crosstalk of DVD and the Space Layer>

The space layer of the DVD is set to be 40 to 70 μm, while the reflectivity thereof is 18 to 30%. This means that the regulation of the reflectivity including the space layer crosstalk is achieved even if the space layer distance is a minimum of 40 μm. That is, the deterioration of signals due to the crosstalk does not matter even if the layer crosstalk increases to (30%/18%)≅1.67. This means that if the ratio of difference in reflectivity between the DVD layers (L0) 75 and (L1) 77 is low, the range of the layer crosstalk can be the same as the range of originally designed values even when the space layer distance (the first space layer 76) is reduced correspondingly.

Now, if the reflectivities of the DVD layers (L0) 75 and (L1) 77 are in equal ratio, the space layer distance (the first space layer 76) can be reduced to 40 μm/√{square root over ((1.667))}=31 μm

with the same layer crosstalk.

Now, to be more practical, if the ratio between the reflectivities of the DVD layers (L0) 75 and (L1) 77 is limited to 1.15 or less, the space layer distance (the first interlayer 76) is 40 μm/√{square root over ((1.667/1.15))}=33.2 μm

so that the layer crosstalk can be the same even when the distance is reduced from 40 μm of the DVD standard to 33 μm.

On the other hand, the thickness of the space layer 36 of the dual layer HD DVD is 15 to 25 μm in the HD DVD standard. When the crosstalk has the worst value, the space layer serving as a bonding layer has a small thickness of 15 μm, and it is thus considered that a further reduction in thickness is not so preferable in light of bonding strength.

The formation accuracy of the first signal substrate is calculated at ±8 μm in the example described above, but it is presumed that the value can be smaller than ±8 μm if the formation accuracy and the accuracy of the stamper are increased in the future. Further, it can be expected that the bonding accuracy and the formation accuracy by 2P are also improved in the future. On the other hand, the reflectivities of the L0 layer and L1 layer are decided by the accuracy of a sputter device, and the ratio therebetween can be brought as close to 1 as possible. Therefore, the space layer distance between the L0 layer and L1 layer can be selected from 31 μm to 40 μm depending on the manufacturing accuracy.

<Reflectivities of the Respective Layers>

In an actual optical disc, in addition to the position of the recording layers when viewed from the light incidence plane, the following is required: the reflectivities of the DVD layers (L0) 75 and (L1) 77 when read with a red laser beam satisfy 18 to 30% of the standard and the difference between the reflectivities is 1.15 or less; and the influence of the HD DVD layer (L2) 81 on the DVD layer (L1) 77, that is, the reflectivity of the HD DVD layer (L2) with respect to the red laser beam is below 8% in the Twin format disc.

On the other hand, when the disc is read with the blue-violet laser beam, it is required that the reflectivity of the HD DVD layer (L2) 81 be 14 to 28% as in the twin format disc, that the maximum value of the reflectivity of the DVD layer (L1) 77 be 28% or less, and that the ratio between the reflectivities of the DVD layers (L1) 77 and the HD DVD layer (L2) 81 be 30%/18%=1.67 or less.

In the embodiment of the present invention, a disc configuration will be shown wherein an Ag alloy film is used for the reflection film of the DVD layer and an Al alloy film is used for the reflection film of the HD DVD recording layer in order to satisfy the conditions described above. Reflection loss in the light incidence plane 71 is 10% in double pass for simplicity concerning the red laser beam and the blue-violet laser beam. Moreover, the birefringence of the disc is 60 nm in the same double pass as the double pass in the HD DVD-ROM standard. The loss is a maximum of 20% for the blue-violet laser beam, and a maximum of 8.2% for the red laser beam. The final result is considered.

FIGS. 9A and 9B show actual measurement values of the reflectivity and transmissivity of the Ag alloy film when its thickness is changed, wherein FIG. 9A concerns the red laser beam (650 nm) and FIG. 9B concerns the blue-violet laser beam (405 nm). FIGS. 10A and 19B show the reflectivity and transmissivity of the Ag alloy film calculated on the basis of the above actual measurement values, wherein FIG. 10A concerns the red laser beam (650 nm) and FIG. 10B concerns the blue-violet laser beam (405 nm). The calculations below were carried out using the reflectivity and transmissivity in FIG. 10.

FIG. 11 shows the relationship between light reflected from the respective layers and the reflectivity thereof when the red laser beam (Ir) 20 has entered the optical disc 70 of the present invention. The reflectivities of the respective layers can be calculated by use of the reflectivities and transmissivities of the respective recording films. However, the loss in the incidence plane is 10%, and the effects of the birefringence are considered later and are not included in these equations.

The reflectivity of the DVD layer (L0) 75: Rr0=Ir0/Ir≅0.9×rr0  (1)

The reflectivity of the DVD layer (L1) 77: Rr1=Ir1/Ir≅0.9×(tr0)²×rr1  (2)

The reflectivity of the HD DVD layer (L2) 81: Rr2=Ir2/Ir≅0.9×(tr0)²×(tr1)²×rr2  (3)

In the same manner, FIG. 12 shows the relationship between light reflected from the respective layers and the reflectivity thereof when the blue-violet laser beam 40 has entered the optical disc 70 of the present invention. The reflectivities of the respective layers can be calculated by use of the reflectivities and transmissivities of the respective recording layers. However, the loss in the incidence plane is 10%, and the effects of the birefringence are considered later and are not included in these equations.

The reflectivity of the DVD layer (L0) 75: Rb0=Ib0/Ib≅0.9×rb0  (4)

The reflectivity of the DVD layer (L1) 77: Rb1=Ib1/Ib≅0.9×(tb0)²×rb1  (5)

The reflectivity of the HD DVD layer (L2) 81: Rb2=Ib2/Ib≅0.9×(tb0)²×(tb1)²×rb2  (6)

One specific example of a design of the present invention will be shown below.

A calculation is made using FIGS. 10A and 10B, wherein (a) the thickness of the Ag alloy film of the L0 layer is 9 nm, (b) the reflectivities of the L0 layer and the L1 layer have the same value, and (c) an Al alloy film is used for the reflection film of the L2 layer (here, in the Al alloy film, rr2=73.1% as to the red laser beam, and rb2=73.7% as to the blue-violet laser beam).

When the red laser beam has entered,

Rr0≅23.5% (rr0=26.1%) from Equation (1)

Rr1≅23.3% (tr0=69.3%, rr1=53.8%) from Equation (2)

Rr2≅5.2% (tr1=40.5%, rr2=73.1%) from Equation (3)

When the blue-violet laser beam has entered,

Rb0≅7.5% (rb0=8.4%) from Equation (4)

Rb1≅14.9% (tb0=85.8%, rb1=22.5%) from Equation (5)

Rb2≅22.9% (tb1=68.5%, rb2=73.7%) from Equation (6)

The results of these calculations are shown in Table 1. (a) concerns a case without birefringence, and (b) concerns a case with a maximum birefringence of 60 nm (it decreases by 8.2% for the red laser beam and decreases by 20% for the blue-violet laser beam). As understood from this table, the regulations of the dual layer DVD disc and the HD DVD disc are satisfied.

Red laser Blue-violet Recording layer beam laser beam (a) Without birefringence DVD layer (L0) 75 23.5%  7.5% DVD layer (L1) 77 23.3% 14.9% HD DVD layer (L2) 81 5.2% 22.9% (b) With a maximum birefringence of 60 nm DVD layer (L0) 75 21.6%   6% DVD layer (L1) 77 21.4% 11.9% HD DVD layer (L2) 81 4.8% 18.3%

It is to be noted that a decrease of reflectivity due to the incidence plane 71 of the optical disc is set at 10%, but the results in Table 1 can be increased to a little less than a maximum of 10% if anti-reflection coating or the like is employed.

<Layer Crosstalk>

It is understood from Table 1 that when the red laser beam 20 has entered the optical disc of the present invention, the layer crosstalk from the HD DVD layer (L2) 81 to the DVD layer (L1) 77 is 4.8 to 5.2%, which is sufficiently lower than 8% required in the twin format disc and does not matter.

On the other hand, it is understood that when the blue-violet laser beam 40 has entered, the layer crosstalk from the DVD layer (L1) 77 to the HD DVD layer (L2) 81 is 11.9 to 14.9%, which is lower than 18.3 to 22.9% in the HD DVD layer (L2) 81 and does not matter.

Next, an examination is made of how the reflectivity with the red laser beam 20 changes with the changes in the thickness of the DVD layers (L0) 75 and (L1) 77. In this change of reflectivity, it is required that the ratio between the reflectivities be 1.15 or less because the thickness of the first space layer 76 is reduced from 40 nm to 33 nm.

When there is a change of ±0.3 nm (a practically larger value) in a thickness of 9 nm of the Ag alloy film of the DVD layer (L0) and in a thickness of 16 nm of the Ag alloy film of the DVD layer (L1), a calculation is made of how much the reflectivities of the DVD layer (L0) 75 and the DVD layer (L1) 77 change.

The reflectivity and transmissivity of the DVD layer (L0) 75

8.7 nm: rr0=24.81% tr0=70.68%

9.3 nm: rr0=27.39% tr0=67.92%

The reflectivity and transmissivity of the DVD layer (L1) 77

15.7 nm: rr1=52.75% tr1=41.82%

16.3 nm: rr1=54.76% tr1=39.84%

where Rr0 and Rr1 are:

Rr0=22.33 to 24.65%

Rr1=21.9 to 24.62%

and the ratio between the reflectivities of the two recording layers satisfies 1.126 in the worst case, and satisfies 1.15 or less. Thus, it is apparent that even when there is a change in the film thickness, the ratio of the reflectivities between the two layers is 1.15 or less even if the distance (the first space layer 76) between the DVD layers is reduced from 40 μm to 32 μm, and the layer crosstalk does not matter.

<Flag Information>

Next, a set of flags in the optical disc of the present invention will be explained. The optical disc of the present invention has two DVD layers, so that in the ID composed of four bytes of the Data Frame of the recording layers (L0) 75 and (L1) 77, bit positions b29 and b24 are written as

b29 (reflectivity): 1b (reflectivity is 40% or less)

b24 (layer number): 0b (in the case of the recording layer (L0))

1b (in the case of the recording layer (L1)).

b6b5 of (BP2) of the PFI in the Control Data Zone (CDZ) in the Lead-in area formed in the DVD layer (L0) 75 indicates the number of layers in the disc, so that

b6b5 (number of layers): 01b (two layers) is written.

Moreover, (BP16) indicates the presence of the BCA, and there must not be the BCA in a DVD video, so that

b7 (BCA flag): 0b (without BCA) is written.

On the other hand, since the HD DVD layer (L2) 81 needs to be treated as a single layer HD DVD disc with low reflectivity, ID composed of four bytes of the Data Frame is written as

b29 (reflectivity): 1b (reflectivity is 40% or less)

b24 (layer number): 0b (recording layer (L0)).

b6b5 of (BP2) of the PFI in the Control Data Zone (CDZ) in the Lead-in area formed in the HD DVD layer (L2) 81 indicates the number of layers in the disc:

b6b5 (Number of layers): 00b (one layer) is written.

(BP16) indicates the presence of the BCA, so that

b7 (BCA flag): 1b (with BCA) is written.

Furthermore, in the HD DVD/DVD Twin format disc, there are regulations of the twin format disc for the conventional single layer DVD and single layer HD DVD, so that (BP33) includes

Layer 0 (b5-b3): 100b (DVD-ROM format)

Layer 1 (b2-b0): 000b (HD DVD-ROM format).

Note that since the disc of the present invention has a triple-layer structure, this regulation for the dual layer structure is not applied. However, it can be judged that there are two DVD layers if the DVD layers are accessed, and it is therefore possible to use the regulation as it is.

However, it is truly more convenient if it can be recognized that there are two DVD layers when the HD DVD layer is accessed. In this case, for example, 101b (dual layer DVD-ROM format) has only to be newly defined in layer 0 (b5-b3).

Next, flag information of the BCA will be explained. A BCA record of the HD DVD has 8 bytes, and (BP4) indicates a book type and a disc type. Since a Twin format flag indicating the twin format disc is in b2 therein,

b2 (Twin format flag): 1b (Twin format disc) is written.

<Reproduction by an Optical Disc Apparatus Complying with the DVD Standard>

Next, a case where the optical disc of the present invention is played back on a conventional DVD player will be explained using FIGS. 13, 14 and 15. FIG. 13 shows the main configuration of a well-known conventional DVD player. FIG. 14 is a flowchart to help explain the operation of the DVD player. FIG. 15 shows focus signals and a focus servo.

A spindle motor 100 rotates/drives a turntable. A damper 101 holds the optical disc 70 onto the turntable. The spindle motor 100 is controlled by a motor driver 102. An optical head 110 includes the objective lens 21 and an optical system 113. The optical system 113 is driven by a focus and tracking actuator 116. When the focus and tracking actuator 116 is controlled by an actuator driver 118, the laser beam is focused on a track on the optical disc and follows the track. A radial actuator 117 is used to move the optical head 110 in the direction of radius of the disc and is controlled by the actuator driver 118.

The reflected light from the disc is taken out of the optical system 113 and is converted into an electric signal at a photodetector in a conversion unit 115. The electric signal is gain-adjusted at a reproduced signal amplifier in a gain adjusting unit 120 and the resulting signal is input to a signal processing circuit 130. The signal processing circuit 130 performs a demodulating process, buffering, error correction, and others and inputs the resulting signal to a data processing circuit 140. Here, the data processing circuit 140 performs packet separation, control signal separation, and the like and inputs video and audio information to an AV decoder 150. The video signal, audio signal, sub-video signal, and the like demodulated at the AV decoder 150 are output as a baseband signal via an AV amplifier 160, and input to a monitor.

Using a focus error signal and tracking error signal obtained by, for example, numerically processing the reproduced signal from a 4-quadrant photodiode, a servo controller 170 supplies a control signal to the actuator driver 118. In response to a signal from an input terminal (e.g., a remote controller or an operation key input section) 190, a system controller 180 controls the playback, stop, and temporary stop of the apparatus, and the like. In addition, the system controller 180 controls a laser diode driver in the gain adjusting unit 120. The laser diode driver drives the laser diode installed in the optical head 110, thereby outputting a laser beam.

When the optical disc 70 of the present invention is inserted in the DVD player, the spindle motor 100 is rotated until a specific number of revolutions has been reached (in step 200 in FIG. 14). Next, the red laser beam 20 is turned on, and a periodic driving current is caused to flow through the focus actuator (ACT) 116, thereby moving the optical head up and down in the direction of axis (in steps 201 and 202 in FIG. 14). A focus signal 203 produced from the reproduced signal periodically appears (see FIG. 15). The lowest reflectivity of the dual layer DVD is 18%, so that if an FS detection level 204 of about 9% is set, two detection pulses 207 are obtained in a focus detection signal 206 (in steps 205 and 207 in FIG. 14).

From the fact that the two pulses have been detected, this disc is judged to be a dual layer DVD (an actual judgment is made by the Physical Format Information (PFI) described later), thereby entering a sequence to play back the dual layer DVD (in step 208 in FIG. 14).

It is to be noted that the FS detection level 204 is set at about 7% lower than 9% in some DVD players. Even in that case, the optical disc of the present invention is not erroneously detected as a triple layer disc because the reflectivity of the HD DVD layer is 5.3% or less.

After a gain adjustment 210 of the reproduced signal is first made (in step 210 in FIG. 14), the DVD layer (L0) 75 is focused on (in step 214 in FIG. 14). After a short stabilization time has elapsed, the recording layer (L0) 75 is in focused-on state (in step 204 in FIG. 14).

Then, when a suitable position of the disc is tracked on (in step 220 in FIG. 14), the reproduced signal can be read. The optical head 110 is located at a given position of the disc, and reads the ID of the data frame of the reproduced signal, thereby making it possible to judge whether the recording layer is the recording layer (L0) or (L1) and whether the position is in a data area or in the Lead-in area, and also to know the set reflectivity (in step 221 in FIG. 14).

Next, the radial ACT 117 is driven, and the optical head is moved to the lead-in area (in step 222 in FIG. 14), and then the PFI in the Control Data Zone (CDZ) is read (in step 223 in FIG. 14). Here, (BP2) is checked to verify that the disc is a dual layer DVD disc, which is followed by the reproduction of dual layer DVD images (in step 226 in FIG. 14). The user can enjoy the DVD images using the input terminal 190.

<Reproduction by an Optical Disc Apparatus Complying with the HD DVD Standard>

Next, a case of an HD DVD player using the blue-violet laser beam will be explained using FIGS. 16, 17 and 18. FIG. 16 shows the main configuration of the HD DVD player. FIG. 17 is a flowchart to help explain the operation of the HD DVD player. FIG. 18 shows focus signals and a focus servo. The configuration of the HD DVD player is similar to that of the apparatus shown in FIG. 13, and the same numerals are therefore given to similar parts.

When the optical disc 70 of the present invention is inserted in the HD DVD apparatus, a spindle motor 100 is rotated until a specific number of revolutions has been reached (in step 200 in FIG. 17). Next, the blue-violet laser beam 40 is turned on (in step 231 in FIG. 17), and a periodic driving current is caused to flow through a focus actuator ACT 116, thereby moving an optical head up and down in the direction of axis (in step 232 in FIG. 17). A focus signal 233 produced from a reproduced signal periodically appears (see FIG. 18).

The lowest reflectivity of the dual layer HD DVD is 18% which is similar to that of the dual layer DVD, so that if an FS detection level 234 is set at about 9%, two detection pulses 237 are obtained in a focus detection signal 236. Moreover, three pulses can sometimes be obtained (in steps 235 and 237 in FIG. 17). Therefore, this disc is temporarily judged to be a dual layer HD DVD disc, a Twin format disc (TFD) or an optical disc of the present invention (in step 238 in FIG. 17), thereby entering a sequence to play back the disc of the present invention (a final judgment is made in accordance with the PFI and the flag information of BCA).

After a gain adjustment of the reproduced signal is first made (in step 240 in FIG. 17), the HD DVD layer (L2) 81 is focused on (in step 244 in FIG. 17). After a short stabilization time has elapsed, the layer (L2) 81 is in focused-on state (in step 245 in FIG. 17). Then, when a suitable position of the disc is tracked on (in step 250 in FIG. 24), the reproduced signal can be read. The optical head 110 is located at a given position of the disc, and reads the ID of the Data frame of the reproduced signal, thereby making it possible to judge whether the layer is the recording layer (L0) 35 or (L1) 37 of the dual layer HD DVD or a single layer (SL) and whether the position is in the data area or in the Lead-in area, and also to know the set reflectivity (in step 251 in FIG. 17).

If, here, the layer is identified as the (L1) instead of the (L0) or (SL), this disc is a dual layer HD DVD, thereby moving to a flow 260 (not shown here) of the dual layer HD DVD.

When the disc is judged to be the L0 or SL, the radial ACT 117 is driven, and the optical head is moved to the System Lead-in area (in step 252 in FIG. 17), and then the PFI in the Control Data Zone (CDZ) is read (in step 253 in FIG. 17). Here, it can be recognized from (BP2) that the disc is an HD DVD single layer disc, from (BP16) that the disc has a BCA, and from (BP33) that a DVD layer is formed in this disc. Subsequently, when the BCA is read (in step 254 in FIG. 17), it is finally verified from the (BP4) of BCA record ID that the disc is an optical disc of the present invention (in step 255 in FIG. 17), which is followed by the reproduction image on of HD DVD layer (in step 256 in FIG. 17). The user can enjoy the HD DVD images using an input terminal 190.

<Reproduction by an Optical Disc Apparatus Complying with Both the HD DVD Standard and the DVD Standard>

Next, a compatible player according to the present invention using both the blue-violet laser beam and the red laser beam will be explained using FIGS. 19 and 20. FIG. 19 shows the configuration of the compatible player. FIG. 20 is a flowchart to help explain the operation of the compatible player. The compatible player can selectively output the red laser beam and the blue-violet laser beam. The parts similar to those in the previously described players are given the same numerals.

First, a disc of the present invention is inserted in the compatible player, and the disc is rotated (in step 200 in FIG. 20). Next, the laser is turned on to move on to focusing/tracking, signal reproduction and image reproduction, wherein the blue-violet laser beam is first turned on (in step 231 in FIG. 20) to reproduce the images in the HD DVD layer.

The reproduction flow for the HD DVD images is the same as that in FIG. 17. The HD DVD layer (L2) 81 is focused on (in step 244 in FIG. 20). Then, the disc is tracked on (in step 250 in FIG. 20). The Data Frame ID, the PFI of the System Lead-in area, and the BCA are read, thereby judging that this disc is an optical disc of the present invention and reproducing the images of the HD DVD. The user can enjoy the HD DVD images using an input terminal 190.

Next, when the user specifies the playback of the DVD by use of the input terminal 190, the red laser is turned on by a signal 261 to switch to the DVD (in step 201 in FIG. 20). This is followed by the same operation flow as that in FIG. 14, so that a focus actuator ACT 116 is driven, the recording layer is searched (in step 202 in FIG. 20), the DVD layer (L0) 75 is focused on, and the disc is tracked on (in step 220 in FIG. 20), thereby reproducing the dual layer DVD images (in step 226 in FIG. 20).

Next, when the user again specifies the playback of the HD DVD by use of the input terminal 190, the blue-violet laser is turned on by a signal 262 to switch to the HD DVD playback (in step 231 in FIG. 20), such that the HD DVD images can be reproduced in a manner previously shown (in step 256 in FIG. 20).

As described above, according to the present invention, the HD DVD and the dual layer DVD can be formed in one optical disc. In the existing DVD apparatus, the dual layer DVD layer is played back. In the HD DVD apparatus compatible with the HD DVD standard, the HD DVD layer is played back. In the compatible apparatus according to the present invention, both the DVD layer and the HD DVD layer can be played back. It is thus possible to allow compatibility between a group of products of the existing DVD standard and a group of products of the new HD DVD standard, and also to accelerate a smooth spread of the HD DVD standard product group to general users.

Other Embodiments

In the embodiment described above, the translucent films of the first recording layer and the second recording layer are formed of an Ag alloy. However, if reflectivity and transmissivity can be selectively set for each of the two laser beams different in wavelength, the apparatus can be more efficiently operated.

For example, the first recording layer and the second recording layer can be formed of multiple interference films to set a more effective reflectivity.

Furthermore, all the recording layers described are playback-only (ROM) recording layers in the present invention, but the combination of the recording layers is not limited thereto. For example, the third recording layer may be a recordable type. In that case, the reflectivity of the third recording layer is reduced to less than half of that in the case of the ROM.

<Summary of Basic Points in the Embodiment Described Above>

An optical disc according to the present invention is basically specified by the following items (1) to (7).

(1) The optical disc is a single-sided triple layer optical disc where a light transmission layer, a first recording layer and a second recording layer which are accessed with a first laser beam, and a third recording layer which is accessed with a second laser beam are arranged in that order in the direction in which the laser beam enters.

(2) The distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm.

(3) The distance between the first recording layer and the third recording layer is a maximum of 72 μm.

(4) The distance between the second recording layer and the third recording layer is a minimum of 15 μm.

(5) The distance between the first recording layer and the second recording layer is about 31 to 40 μm.

(6) The reflectivities of the first recording layer and the second recording layer with respect to the first laser beam are 18% or more, and the ratio between the reflectivities is about 1.15 or less.

(7) The areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer.

Furthermore, the optical disc according to the present invention can additionally implement the following item (8) on the basis of the above items:

(8) The reflectivity of the third recording layer with respect to the second laser beam is 14 to 28%.

An optical disc apparatus according to the present invention is specified by the following items (9) to (15):

(9) The optical disc apparatus is an apparatus which reads information recorded on an optical disc.

(10) The optical disc is a single-sided triple layer optical disc where a light transmission layer, a first recording layer and a second recording layer which are accessed with a first laser beam, and a third recording layer which is accessed with a second laser beam are arranged in that order in the direction in which the laser beam enters.

(11) The distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm.

(12) The distance between the first recording layer and the third recording layer is a maximum of 72 μm.

(13) The distance between the second recording layer and the third recording layer is a minimum of 15 μm.

(14) The distance between the first recording layer and the second recording layer is about 31 to 40 μm.

(15) The reflectivities of the first recording layer and the second recording layer with respect to the first laser beam are 18% or more, and the ratio between the reflectivities is about 1.15 or less.

(16) The areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer.

(17) The information reading apparatus comprises an optical head which can generate the first laser beam and the second laser beam, and control means for causing the first laser beam or the second laser beam to be selectively generated.

Furthermore, the optical disc apparatus according to the present invention can additionally implement the following item (18) on the basis of the above items:

(18) The reflectivity of the third recording layer with respect to the second laser beam is 14 to 28%.

Furthermore, the optical disc apparatus according to the present invention can additionally implement the following item (19) on the basis of the above items:

(19) When the optical disc is inserted, the second laser beam is first turned on to access the third recording layer.

Furthermore, the optical disc apparatus according to the present invention can additionally implement the following item (20) on the basis of the above items:

(20) The control means selects the first laser beam or the second laser beam in accordance with a user input from a user interface.

It is to be noted that the present invention is not limited to the embodiment described above without modification, and some of all the components shown in the embodiment may be eliminated. Moreover, components in different embodiments may be suitably combined.

According to the embodiment described above, it is possible to provide an optical disc which enables a first recording layer and a second recording layer (corresponding to a dual layer DVD layer) to be accessed with a first laser beam (red laser beam) and enables a third recording layer (corresponding to an HD DVD layer) to be accessed with a second laser beam (blue-violet laser beam) from one side. Therefore, a single optical disc can contain both movie content for the currently widespread dual layer DVD disc, and movie content for the HD DVD. As a result, it is possible to record on this optical disc most of the movie content (generally consisting of a feature film and bonus content) which have already been provided or which will be provided in DVDs, thereby providing a real combination disc which can deal with both standard (SD) images and high definition (HD) images.

Furthermore, DVD content can be reproduced in conventional DVD compatible optical disc apparatus. On the other hand, the new HD DVD compatible optical disc apparatus can be adapted to be able to reproduce the movie content for the HD DVD or to reproduce both the movie content for the HD DVD and the movie content for the DVD.

For example, identical movie contents are prepared as DVD content and HD DVD content, and if these two movie contents are recorded on a single disc, a user who has a DVD compatible apparatus alone can see the DVD movie content, while a user who has an HD DVD compatible apparatus can see the HD DVD movie content.

If the user who does not presently have an HD DVD compatible apparatus purchases an HD DVD compatible apparatus in the future, he/she can enjoy the HD images with an already purchased optical disc without newly purchasing an HD DVD disc, which is a great advantage to the user.

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A single-sided triple layer optical disc comprising: a light transmission layer; a first recording layer and a second recording layer which are accessed with a first laser beam; and a third recording layer which is accessed with a second laser beam, these layers being arranged in that order in a direction in which the laser beams enter, wherein the distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm, the distance between the first recording layer and the third recording layer is a maximum of 72 μm, the distance between the second recording layer and the third recording layer is a minimum of 15 μm, the distance between the first recording layer and the second recording layer is about 31 to 40 μm, the reflectivities of the first recording layer and the second recording layer with respect to the first laser beam are 18% or more, the ratio between the reflectivities being about 1.15 or less, and the areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer.
 2. The optical disc according to claim 1, wherein the reflectivity of the third recording layer with respect to the second laser beam is 14 to 28%.
 3. An optical disc apparatus which reads information recorded on an optical disc, the optical disc being a single-sided triple layer optical disc comprising: a light transmission layer; a first recording layer and a second recording layer which are accessed with a first laser beam; and a third recording layer which is accessed with a second laser beam, these layers being arranged in that order in a direction in which the laser beams enter, wherein the distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm, the distance between the first recording layer and the third recording layer is a maximum of 72 μm, the distance between the second recording layer and the third recording layer is a minimum of 15 μm, the distance between the first recording layer and the second recording layer is about 31 to 40 μm, the reflectivities of the first recording layer and the second recording layer with respect to the first laser beam are 18% or more, the ratio between the reflectivities being about 1.15 or less, and the areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer, the information reading apparatus comprising: an optical head which is configured to generate the first laser beam and the second laser beam; and control means for causing the first laser beam or the second laser beam to be selectively generated.
 4. The optical disc apparatus according to claim 3, wherein when the optical disc is inserted, the second laser beam is first turned on to access the third recording layer.
 5. The optical disc apparatus according to claim 3, wherein the control means selects the first laser beam or the second laser beam in accordance with a user input by a user interface.
 6. An optical disc apparatus which reads information recorded on an optical disc, the optical disc being a single-sided triple layer optical disc comprising: a light transmission layer; a first recording layer and a second recording layer which are accessed with a first laser beam; and a third recording layer which is accessed with a second laser beam, these layers being arranged in that order in a direction in which the laser beams enter, wherein the distance of the light transmission layer from a light incidence plane to the first recording layer is a minimum of 550 μm, the distance between the first recording layer and the third recording layer is a maximum of 72 μm, the distance between the second recording layer and the third recording layer is a minimum of 15 μm, the areal recording density of the third recording layer is three times or more as high as the areal recording density of the first recording layer and the second recording layer, the distance between the first recording layer and the second recording layer is about 31 to 40 μm, the reflectivities of the first recording layer and the second recording layer with respect to the first laser beam are 18% or more, the ratio between the reflectivities being about 1.15 or less, and the reflectivity of the third recording layer with respect to the second laser beam is 14 to 28%, the information reading apparatus comprising: an optical head which is configured to generate the first laser beam and the second laser beam; and control means for causing the first laser beam or the second laser beam to be selectively generated.
 7. The optical disc apparatus according to claim 6, wherein when the optical disc is inserted, the second laser beam is first turned on to access the third recording layer.
 8. The optical disc apparatus according to claim 6, wherein the control means selects the first laser beam or the second laser beam in accordance with a user input by a user interface. 